Ocean island volcanoes are generally characterised by the relatively quiet extrusion of basaltic lavas, although more violent activity can and does occur, particularly in the Ascencion, Canary, and Cape Verde archipelagos of the African Atlantic. Others, such as Reunion are far from any plate margin, and sit above hot spots in the earth's crust where plumes of magma rise from deep within the interior of the planet.
PIC: The 1977 eruption of Karthala(Comoros)
World-wide, just over a hundred oceanic volcanoes have managed to grow, like Reunion and Comoros, large enough to penetrate the surface of the sea and form islands, but many thousands more remain hidden beneath the waves.
The following volcanic islands around Africa are described below:
* Canary Islands
* Cape Verde
* Tristan de Cunha
* Marion Island
KARTHALA, Comoro Islands, Indian Ocean
Twenty two million years ago, a hot spot plume started erupting five kilometres beneath the Indian Ocean. For another ten million years liquid rock continued welling from the mantle until the summit emerged above the surface of the sea about 12 million years ago. The first of these mountain peaks to appear was the island of Mayotte.
The youngest and largest island, Grande Comoro, is made of two active coalescing shield volcanoes, Karthala and Massif de la Grille. Both volcanoes have erupted in historic times. Karthala, with an altitude of 2314m, is the most active and has erupted many times in past few decades. The most recent activity at this volcano was a phreatic explosion in 1991. Some 12 nautical miles to the west of Grand Comoro lies a submerged volcano Banc Vailheu, now extinct.
The surrounds of the Kartala crater are rocky with bracken and giant heathers vegetation. The summit is quite cold due to the ever-present mist. The summit clouds occasionally break away exposing the giant crater. The crater complex consists of a small crater called Choungou Chagnoume and a large crater called Choungou Chahale. On the bottom of the small crater, is a smoking sulphuric lake. The lake changes colours as the rays of sun strike it at different angles, from shadowy grey to aquamarine and then deep green in the late afternoon. This is the sight of more recent eruptions, with the fumaroles still emitting a trail of steam. Judging the size of the craters (6x3 km), at least one full day would be needed to explore the summit complex.
Karthala last major eruption was in 1977, followed by small eruptions in 1986 and 1991. Its tempestuous personality is monitored by three seismic stations located at the summit and a central station located in the capital city of Moroni. A lava flow during the 1977 eruption destroyed the coastal village of Singani on the south-western side of the island. The last 1991 eruption did not spew any lava and was limited only to a phreatic explosive activity within the crater, shooting out rocks and releasing sulphuric gases down onto the island slopes.
The active volcano Karthala occupies two thirds of the southern part of the Grand Comoro island. The principal structural traits of the basaltic volcano are tied to the existence of two rift zones, facing from opposite side of a summit caldera. Phreatic and phreatomagmatic eruptions have been reported on various occasions or registered by the monitoring stations. During the historic period most of the eruptions took place along south-east rift zones and north of the volcano or in the summit caldera. In August 1918, two major explosions occurred with the expulsion of ashes reaching more than 4000m in height. Only the April 1977 eruption, the last magmatic eruption of Karthala, took place at a low altitude on the south-sothwestern side of the volcano, outside the axis of fracturation.
The La Grille volcano is a total disappointment in volcanological terms as the typical volcanic barren landscape is completely absent. It is, however, a paradise for naturalists as it features ever-misty rain forest. Volcanic cones that are weathered to mere hills with a nutrient-rich, black soil dot the summit.
The famous sightseeing is a beautifully positioned volcanic crater of Lac Sale (Salt Lake) on the northern tip of the island. The crater grew from the beach along a fissure line. The fissure line, dotted by volcanic cones, is apparently stretching from the volcano La Grille down to the sea. The unfinished stratovolcanic structure indicates that the volcano blew its top (unlike the other craters up in the mountains) in an enormous explosion, probably due to leaking seawater into the active crater. The algae-rich water of the lake changes colour twice a day; from a deep green to a shimmering blue.
On the south-western side of the island lies the village of Singani. The spectacular coast here consists of sheer volcanic cliffs with deep caves and blowholes. In 1977, the Karthala flank opened, leaking fountains of flaming lava. Lava flows quickly reached the village, forcing people to run for their lives. For days, the inhabitants hopelessly watched as the volcano claimed their homes. Singani was split in two by lava flows, which were running through the village toward the sea. Most of its residents rebuilt their houses in exactly the same places as before because they believe that lava never flows twice over the same place.
PITON DE LA FOURNAISE, Reunion, Indian Ocean
La Fournaise was born from a hot spot - a phenomenon linked to plate tectonics. The island of Reunion, 700 km east of Madagascar, is the work of a single bloom of magma burning its way across the African continental plate. The Hawaiian volcanoes are also a good example of this phenomenon. The hot spot, which marked the birth of Reunion, is also responsible for the formation of the neighbouring island of Mauritius.
From the time of island colonisation in 1665, La Fournaise has erupted more than 200 times. Volcano and its lunar landscape are the major tourist attraction. A basaltic shield volcano, Piton de la Fournaise forms the south-eastern part of Reunion,. Three calderas formed at around 250 000, 65 000 and 5000 years ago by progressive eastward slumping of the volcano. Most historical eruptions originated from the summit and flanks of a 400m high lava shield that grew within the youngest caldera. The main cone is summitted by the smaller crater Bory and a huge crater Dolomieu. The Bory crater has been inactive since 1971. On the slope of the main cone, tens of minor craters can be seen.
An eruption is always preceded by an increase in seismicity. When earth tremors are located close to the surface, the eruption might take place within the next few days. Certain safety measures are adopted and access to the area is forbidden. Then the authorities prepare to manage the masses of visitors.
The 1998 eruption (witnessed by the author) was one of the longest of this century with 196 days duration from the beginning on March 9, 1998. The emitted volume was estimated at 50 million cubic metres, marking this eruption as one of the most voluminous during this century. Since then the volcano has erupted every year.
Ocean island volcanoes are generally characterised by the relatively quiet extrusion of basaltic lavas, although more violent activity can and does occur, particularly in the Ascencion, Canary, and Cape Verde archipelagos of the African Atlantic. Others, such as Hawaii and Reunion are far from any plate margin, and sit above hot spots in the earth's crust where plumes of magma rise from deep within the interior of the planet. All the Canaries are volcanic islands with Fuertaventura, Lanzarote and Gran Canaria the oldest and Tenerife, La Gomera, El Hierro and La Palma the youngest. The most spectacular badlands caused by eruptions are found on Tenerife, Lanzarote and La Palma.
TEIDE, TENERIFE, Canary Islands
About 170 000 years ago, Tenerife was set for a massive collapse. A huge volcano, more than 4000m high, dominated the island landscape. Immense rift pressure was building and a colossal force was to be unleashed. Empty magma chamber inside the volcano could not support the mass of the mountain anymore. The volcano suddenly collapsed. The collapse triggered landslide that swept away the top of the island and left the ocean floor strewn with gigantic rocks. The post collapse activity gave birth to Teide volcano growing from the horseshoe-like depression.
This volcanic activity is still going on, although centuries of calm elapse between the eruptions. From the coast, desolate hills dominate the landscape of Tenerife and eroded volcanoes drop shear into the sea. Tenerife is a stratovolcano capped by the Las CaÃƒÂ±adas caldera. The caldera is 12x20 km in diameter and is partially filled by Montana Blanca, Pico Viejo (which has a large explosion crater), and Pico del Teide. The summit is made up of dozens of cones of different origins, shapes, sizes and compositions. Two large modern volcanoes, Teide and Pico Viejo are the most important peaks. They have erupted hundred of times over thousands of years and have been formed from successive eruptions of lava and pyroclasts, which accumulated in superimposed layers. Other volcanoes, such as Roques Blancos and Chinyera Mountain, are the result of a single eruption.
The unique feature of the Teide volcano is its extremely blocky lava. Numerous lava blocks reach the size of a double-storey house. The reason for this is that the Teide lava, being relatively cold and therefore very viscous, does not flow easily. The thick magma accumulates on the vent, building a dome, while its surface cools and solidifies. Expanding gases within cause big explosions, but most of the time the magma slowly starts to flow downhill. Due to its almost solid state the crust breaks up into a distorted mass of large blocks.
The crater of Teide is crowned by the Pan de Azucar lava cone, which filled up the ancient La Raubleta crater during a recent eruption, most probably taking place in the middle ages. The crater emits gases through numerous fumaroles. Exhausting but presenting no mountaineering difficulties, the ascent and the descent of the volcano offers stunning vistas and the excellent opportunities to admire the varied nature of the island.
Mt Teide is part of the Pico Teide-Pico Viejo complex formed in the last 175 000 years in the Las Canadas caldera. Pico Teide and Pico Viejo overlap to form an elongate double edifice with a shallow saddle at 3000m. The first eruption of Pico de Teide took place less than 170 000 years ago, a very short time span in geological terms. Since then there have been periods of vigorous activity. Pico de Teide and other vents of Tenerife have erupted several times since the island was settled in 1402. Mt. Teide was belching fire as Columbus passed in 1494 on his way to America and there were further sizeable eruptions in 1604, 1605, 1705, 1706, 1798 and 1909. At present the volcano only emits gases mainly through its numerous fumaroles. Fumaroles represent 85% gases emitted by the mountain. Volcanologists believe Teide will erupt again - the question is when.
Southern part of the caldera is dominated by its highest peak, Montana de Guajara, 2717m, which is the third highest peak on the island. Between Teide and Guajara, fairy-tale rocky formations are slowly emerging when driving down the road. Los Roques de Garcia is a group of characteristic rocky towers particularly enchanting at sunset. During the collapse of the ancient volcano, Roques de Gracia, bolstered by highly resistant dykes and necks, were left jutting out as a spur. The most remarkable formation is the Cathedral Rock that formed during the eruption. Magma, too cold to flow slowly extruded from the bowels of the earth. During the solidification process, the magma contracted and vertical prismatic joints were formed all over the volume. This type of rock structure is generally described as the organ pipe basalts.
No less enchanting are the rocky formations of the Piedras Amarillas rugged peaks, just below the Montana de Guajara, about one km drive from Los Roques. It is probably the most spectacular grouping of pyroclastic debris within the park. The rocks have eroded into incredible, fantastic shapes.
Close to Los Roques, heading south, is the rock formation known as Los Azujelos (glazed tiles), where the rocks glint green with chlorite and epidote deposits. Here, deep within the ancient volcano, a hydrothermal alteration occurred when ground water reached the roots of an active volcano. Volcanic gases dissolved in the water dissolved part of the rock, which was deposited in the form of new minerals. After the volcano landslide, these characteristic greenish rock formations were left exposed. Further south is the great expanse of the Llano de Ucanca. This is one of the park many Candas - yellow sedimentary plains where fine volcanic debris has accumulated over the millennia.
Latest Pico Viejo eruption
Pico Viejo is the second largest volcano on Tenerife Island with an altitude of 3070 metres. The volcano, with its 800m diameter explosive crater has been erupting over thousands of years. The last eruption occurred on June 9, 1798, following two years of earthquakes. It began with a 700m long fissure on its southwestern flank in which several vents opened up. From the upper vents, gases and lava fragments were hurled over 1000 metres into the air. Torrents of incandescent lava poured out from lower vents downhill onto the caldera plains. The eruption lasted 92 days and lava flows covered an area of about five square kilometres. The finest fragments were carried by the wind to the neighbouring islands.
The most recent eruption on Tenerife
The most recent eruption started on Chinyero Mountain on 18 November 1909. The eruptive activity consisted of strombolian explosions and lava flows. Three eruptive cones opened, hurtling large amounts of lava downhill towards the sea. It lasted only ten days, producing lava flows that caused some damage, covering 2.2 sq km.
CUMBRE VIEJA AND TABURIENTE, LA PALMA, Canary Islands
The most recent eruptions on Canary Islands occurred on the island of La Palma in 1949 and 1971. These eruptions were small compared to its earlier eruptions. The explosion that formed the island Caldera de Taburiente, some 400 000 years ago, was enormous; it is from here that the word caldera originates (giant crater formed by the collapse of a volcano). The wedge-shaped island of La Palma, with its summit elevation of 2426 m, contains two large volcanic centres. The north is the place of the massive Caldera Taburiente, while in the south, the Cumbre Vieja rift volcano, has been the site of historical eruptions recorded since the 15th century.
During the 1949 eruption, part of the very steep western flank of Vieja volcano started to slide seaward. The movement stopped after 4 metres but a new eruption could trigger the final push.
An eruption from the southern tip of La Palma started on 26 October in 1971. A 300 m long fissure-fed eruption produced lava flows that reached the southwest coast. In total six vents opened during the eruptive period. The eruption was characterised as intermittent ejection of bombs, scoria bombs and lapilli with more or less viscous lava flows. The fissures emitted abundant white gases at great pressures, rich in sulphur dioxide. Ejection of lava fragments reached at times up to 400 m high. On 18 November 1971, the volcanic activity ceased.
TIMANFAYA (MONTANAS DEL FUEGO), LANZAROTE, Canary Islands
Lanzarote is a strange, enchanting moonscape so unique that the entire island is a World Biosphere Reserve protected by UNESCO. The island is made of a shield volcano consisting of prominent fissure vents. Lanzarote is approximately 16 million years old. There are four main calderas and numerous cones and fissures. This island which has been destroyed so many times by the elemental forces of its volcanoes and reborn again, shows some of the most incredible landscapes you may find on this planet, opulent vegetation next to bizarre forms of petrified lava.
Named after the largest of the volcanoes, Timanfaya National Park or the Mountains of Fire (MontaÃƒÂ±as del Fuego), is an eerie jumble of craters, cinder cones, solidified lava formations and fissures. It is forbidden to leave your car in the area of the park.
At an elevation of 350m, the Montana Rajada vantage point look up upon one of the most impressive sections of the entire region: an immense mass of lava, called the Plain of Timanfaya, covers most of the park extending all the way to the distant shoreline. The row of volcanic cones crowned by dantesque craters stand in the sea of lava, intersected by long and deep hollows of the collapsed roofs of lava tunnels. An unimaginable event left here 300 major craters. The longest fissure is 8 km long, dotted by 32 craters - a dramatic evidence of floods of fire.
An eyewitness account of the catastrophe says that; On the first day of September 1730, around 21h00, the earth suddenly opened close to Timanfaya mountain. During the first night an enormous mountain rose from the bowels of the earth with flames shooting from its summit which continued burning for 19 days. This was the spectacular beginning of volcanic eruptions that continued intermittently for almost six years. A process, which greatly increased the surface area of the island.
The volcanoes, which now form Timanfaya National Park, emitted huge columns of tephra, which carried by the wind, blanketed immense areas and covered the slopes and craters of many of the old mountains. The principle nucleus of the eruptions was the Fuego (fire) mountain that had grown to an altitude of 510m above sea level.
Until 16 April 1736, lava and ash continued to burst from a giant fissure system by a series of 26 volcanic eruptions, eventually covering over 200 sq km.
The eruption destroyed farms and villages, and turned the fertile farmland into a volcanic desert. There were no casualties, but many inhabitants lost everything and were forced to emigrate. As there had only been hamlets and small farming settlements in this region, only 420 houses were destroyed by 6 years-long volcanic onslaughts.
In 1824, the last volcanic eruption took place on Lanzarote. The eruption was preceded by a preparatory period of several years during which the island registered numerous medium-sized earthquakes. The principle characteristics of this eruption were the fluidity of the streams of molten lava and the tall columns of boiling seawater rising from the Tinguaton volcano. The 1824 eruption lasted about three months and was focused at the Nuevo del Fuego vent.
MARION ISLAND: Fire and ice
Created over the millennia from ruthless battle between water and fiery land, Marion Island was forged by an undersea volcano, the earth rising from the dark waters of the Southern Ocean. And this raw, rocky island grew larger and taller. Located in one of the most inhospitable regions of the world - in the roaring forties, it was discovered, named, forgotten and since rediscovered so many times. Witness of human drama, of sinking ships and the slaughter of seals and whales over the past centuries, the island is now an oasis of strict conservation and harsh tranquillity.
ItÃƒÂ¢Ã¢â€šÂ¬Ã¢â€žÂ¢s some 500 000 years ago, an ash-laden steam cloud rises from the deep, caused by volcanic eruptions originating on the seabed. Half-way between the southern tip of Africa and Antarctica, violent explosions mark the birth of this windswept island. With magma and seawater able to mix freely, the explosions are nearly continuous. When the infant volcano appears above the waves, vigorous lava fountains take over, causing widespread capping of fresh lava that protects the loose ash and cinders from the continuous pounding of the ocean waves. Rivers of lava start to claim the territory that has previously been the domain of the ocean.
Just over a hundred oceanic volcanoes world-wide have managed to grow, like Marion, large enough to penetrate the surface of the sea, forming islands, but many thousands more remain hidden beneath the waves. When a volcanic island first emerges, the new land surface is devoid of any form of life. The process of migration to Marion Island began thousands years ago yet the biota still gives the impression of being impoverished and in a state of disharmony. The first life on the island not only had to face the dangers of prolonged volcanic activity but also the hazards of extensive glaciations.
Marion Island, South Africa's only historically active volcano, lies at the southwestern end of a submarine plateau immediately south of the Mid-Indian Ocean Ridge, opposite Prince Edward Island, which together form the Prince Edward Islands Archipelago. The island rises sharply from the sea with rough and uneven coastlines, covering an area of 290 sq kilometres. Most of the shores on the island are rocky and comprise vertical cliffs, whereas there are far fewer boulder beaches and only two sandy ones. The island is really only a pinnacle of an undersea volcanic ridge or spine that sticks out above the sea surface.
At a distance, the island presents a low dome-like profile, broken by several conical hills consisting of volcanic ash and scoriae. Grey clouds envelop high peaks for most of the year. The central highland is an arcuate plateau surmounted by a series of volcanic cones responsible for the serrated skyline of the summit area. The plateau comprises two series of prominent cones aligned along two different trend lines that meet in the vicinity of Jan Smuts Peak (1185m). The highest mountain, State President Swart Peak, rises 1230m above sea level. The plateau has an average elevation of 1000 m above sea level and is covered by a flat, stationary glacier, also known as the ice-plateau.
The weather in general is very cold, cloudy and windy. The annual average temperature is about 5 degrees C, with only about 29% sunshine per year and an annual rainfall of 2500mm per year. There are frequent gales on Marion Island, which lies within the roaring forties latitudes.
The South African government protects this internationally important conservation area to the low-water mark as a Special Nature Reserve. Because of the harsh conditions, Marion ecosystem is fragile. Human interference is kept to a minimum. All refuse is stored throughout the year and then removed to SA mainland. To ensure that opportunity for the introduction of alien insects and plants is limited, no fresh fruit or vegetables are brought to the island.
Marion island is a shield volcano, formed by predominantly basaltic effusions that alternated with explosive eruptions from numerous vents throughout its history. The low profile, 24 x 16km in diameter, the island is dotted by about 150 cinder cones, smaller scoria cones, and coastal tuff cones. More than 130 scoria cones and many lava flows formed during the Holocene (the past 10 000 years).
Essentially there are two main lava types on the island. Grey basalt lava of the First Volcanic Stage, 270 000 to 48 000 years old, is the oldest rock type on the island. A peak of volcanic activity occurred about 100 000 years ago. The rocks of this stage consist of massive lava and intercalated pyroclastics. They built the elevated plateau as well as isolated patches protruding through the younger cover. Individual lava flows vary from less than one metre to about 30 metres in thickness, and are often variable. The paucity of vesicles and their small size in within the lava and its high viscosity (presence of platy joints) suggest that the grey lavas were extruded in water, several thousand metres deep and that Marion Island was elevated to its position after the extrusion of these lavas. Another possibility is that the more massive units in the succession are not lava flows but sills. No evidence of a central eruptive vent has been found. It seems that numerous separate vents existed during the First as well as the Second Volcanic Stages.
Stones of different sizes, large solitary boulders and deep striation in the rocks on grey lava ridges all bear testimony to the ice sheets that scoured Marion Island as recently as 12 000 to 16 000 years ago when temperatures were probably 4 to 7 degrees C lower than they are at present.
The Second Volcanic Stage, that followed the rapid melting of glaciers, has given rise to the black basalt lava formations that dominate much of the island terrain. These rocks date from about 15 000 years ago to very recent, in the vicinity of Kaalkoppie. The conical red and black scoria cones represent the main areas of explosive eruptions and many of the lava flows arose from them. Many pyroclastic cones have also given rise to superficial accumulations of wind-blown ash and lapilli. At a few localities evidence of fumarolic activity was found in the form of scoria fragments cemented by white and yellow crusts.
Some unvegetated lava flows appear no more than a few hundred years old. The younger flows often emanate from the crater or base of a scoria cone but it is clear that the greatest volumes flowed seawards from the highest peaks.
Essentially three kinds of black lava can be found on the island; pahoehoe lava flows with curved ropy structures, aa lava flows covered with loose clinker fragments and blocky lava flows consisting of large angular blocks with sharp edges. Unlike pahoehoe with its internal drainage system, both aa and blocky flows were fed with open lava streams that left behind them U-shaped channels scooped up out of lava which had not yet completely solidified. Such lava channels are numerous and impressive on Marion, between 5 and 15 metres deep and can be followed for up to a kilometre or more.
Marion Island could serve as an object lesson in volcanology; virtually every feature characteristic of basaltic extrusions is present among the younger lava flows and is often in a better state of preservation than similar phenomena in temperate regions.
First eruption in historic time went unnoticed
Although some lava flows had a remarkably fresh appearance, there were no fumaroles and no records of activity in historic time. The island had been considered an extinct volcano until 1980 when a totally unexpected volcanic eruption became the most exciting geological event in its history. During the first week in November 1980, research station personnel visiting the western side of Marion Island observed two new cinder cones, three small lava flows, and fresh tephra deposits, none of which were present when the scientists were last in the area in February.
South African scientists, Russell and Berruti, travelled to the eruption site in late November. Re-growth of burnt vegetation indicated that the activity had probably occurred at least 2 months earlier. The smaller of the two cinder cones, about 6 m high with a crater 15m in diameter, had formed at the summit of Kaalkoppie, which is an eroded, 100-m-high tuff cone. A lava flow, that apparently originated from the western (seaward) flank of the summit cone, had poured over the nearby cliffs, 50-70m high, and ponded in a small amphitheatre-like area at their base. About 10m of lava remained in the amphitheatre in November, but caves above this level were partially filled with lava. Some of the lava had drained from the amphitheatre and continued about 100 m seaward, flowing into the ocean and forming a front 120m wide and 10m high. A lava tube seen at the southern edge of this flow in early November had collapsed by the time Russell and Berruti saw it on the 26th, forming a 4-m-wide trench. This flow covered approximately two hectares, including the portion between the summit cone and the cliffs.
A second lava flow occupied a few hundred square meters of the promontory above the amphitheatre. A small amount of this lava had spilled through a fissure onto the first flow, but most remained on the promontory or poured over its concave northern cliff face into the sea.
On the flank of Kaalkoppie, east of the new summit cone and near its base, a larger tephra cone had formed around a 35m-diameter crater. The eastern side of the cone was breached by a lava flow, 35 m wide as it emerged from the crater, eventually reaching 50m in width before diverging into two lobes. One lobe flowed about 350m to the northwest, the second about 200m to the south along a shallow valley. The total area covered by this flow was approximately seven hectares.
Irregular blocks and spheroidal bombs nearly 1 m in diameter were found on the flank of the cone. Fusiform and ribbon bombs fell as much as 350m from the cone with the heaviest tephra fall extending from its east, breached, side. A continuous layer of ash and lapilli covered an area extending several hundred metres to the east and 40 metres south of the two cones, with scattered fragments found 250 metres to the south and much further to the south-east.
The least accessible volcano
You just cannot get there, unless you own a jet that can land on a wavy sea, or a powerful yacht that can withstand the onslaught of roaring forties. Even then you cannot get there! You need special permission from the South African Department of Environmental Affairs and Tourism, and for that you have to have a very good reason, such as scientific research.
The island is a place of harsh beauty and extreme conditions. It is one of the places on earth that man does not rule. Everything works in natural harmony and it is only a few fortunate scientists and logistic personnel that can experience its tranquillity. The island is uninhabited, except for the temporary employees of the research station that are employed by the South African government for periods of 14 months at a time. Relief voyages to replenish supplies and to exchange personnel take place every year in April-May.
The voyage to Marion Island takes 5 days and passes through some of the stormiest seas in the world. Hairy humans (according to an Antarctic tradition they do not cut their hair nor they shave) greet the newcomers.
There are no roads, no paths. Walking is the only way to get around the island and it takes five days, to cover the 90km. Strategically placed huts, with food and gas supplies, provide shelter. Apart from a fringe of grass on top of the cliffs, the foothills only have a covering of soft, spongy and mossy vegetation, which, together with the high rainfall, create swampy conditions that make hiking difficult.
Lava flows often create major obstacles during hiking. Aa lava flows are the commonest kind on Marion Island. These flows, usually piled up in heaps 5 to 20m high, are tedious to cross even on the lower slopes of the island where they are covered by vegetation. However, the blocky lava flows, usually heaped in chaotic fashion to form steep parallel ridges, make for the most difficult terrain. Various lava tubes and tunnels that make up the pahoehoe flows, and in some areas, volcanic bombs and streamlined lapilli (comet-like solidified rock) can also be seen.
On the edges of the stationary glacier, or ice plateau, large moraines obscure the ice, but wind and water-carved blue ice are characteristic of the glacier itself. During winter, many large caverns, which are caused by meltwater, are covered by only a fine layer of snow, making the ice plateau dangerous.
The few beaches abound with elephant seals amongst the boulders. As may be expected, there are many penguins; hundreds of thousands of these, often referred to as the little chaps in dress suits, sit around in their breeding colonies around the coast. It is possible to hear and smell them from kilometres away. Killer whales regularly visit the coastal waters. There are twenty-eight sub-Antarctic bird species, for example several species of the Petrel family, Albatrosses, Kelp Gulls and sub-Antarctic Skuas. The apparent fearlessness of most animals towards man enhances your feeling of being an intruder in a pristine environment.
The house mouse, introduced from sealing ships as early as 1818, inhabits the marshy, undulating slopes around the coast. To control the mice in the base, five domestic cats were brought to the island in 1948. The cat population increased rapidly, impacting disastrously on the burrowing bird population. In 1975 alone, more than 2000 cats killed an estimated 450 000 petrels. An intense eradication programme followed, taking 15 years to successfully eliminate the feline hunters.
Discovered and forgotten many times
The existence of Marion Island has been known to humans for over three centuries, although the first landing only took place more than 130 years after its discovery. The first mention dates back to 1663, when a Duch East Indian ship passed it en route to Java. The name then given to the island was Maerseveen. No landing was made.
After the discovery, the island had been forgotten, only to be re-discovered by Frenchman Marion du Fresne more than half a century later. The Frenchman, who was searching for Antarctica, named it Terre d Esperance (Isle of Hope) in 1772, mistakenly thinking he had reached the long-sought Southern continent. Due to the bad weather, his attempt to land was unsuccessful. After discovering the mistake and in his disgust, he renamed both islands The Frigid Islands.
Almost five years later, Captain James Cook, not aware of the previous discoveries, named both islands the Prince Edward Islands. He, too, did not attempt to land. After realising that Marion du Fresne had been there, he named the larger island in his honour. It was not until the middle of the 19th century that this larger island was first referred to as Marion Island by sealers.
A wealth of animal life soon sparked an economic interest in the islands. Whalers and sealers began visiting the area in rapidly increasing numbers. Although they were pioneers of their day, they left little to posterity. When and by whom the first landing was made remains a mystery. In 1802 there were already sealers establishments on both islands. Seal slaughtering had reduced the animal population into such extend that the industry died out in 1860. The first scientific observations were made in 1830.
At least eight vessels are said to have foundered, five of them in the vicinity of Prince Edward and three at Marion Island. The most tragic incident happened 1849 when an emigrant ship from England, heading for New Zealand, ran aground. Fifty three of the ship 63 passengers drowned (including 5 women and 10 children). The remaining survivors were rescued after 72 days on the island. It is the only known deaths of women and children at the islands.
Marion Island was annexed by South Africa in 1947 and it was at first purely used as a meteorological station. Research programs are currently also being undertaken in the oceanographical, biological and geological fields. At present, Marion Island has the largest meteorological station in the southern hemisphere.
The pristine neighbour
Prince Edward Island, situated 19 km northeast from Marion, is also a shield volcano. There was no known eruption in historical times. Actually, Marion and Prince Edward islands represent the twin peaks of a coalescing shield volcano, which, although rather sleepy, is still active. It means that there may well be a future eruption on Prince Edward Island. The geology of Prince Edward Island is very similar to that of Marion.
It is smaller (45 sq km), and reaches only half the altitude of Marion. The island has a markedly asymmetric profile, consisting of a Central Block, which ends abruptly at the western escarpment but gradually slopes eastward. The small size and relatively low elevation of the island may have prevented the formation of an ice cap.
Van Zinderen Bakker Peak, the summit of the island (672m), is a flat-topped cone with a shallow crater. Wolkberg, a steep cone with a breached crater, is a source the most extensive and apparently the youngest lava flow. The explosive activity of this cone is well demonstrated by its steepness, the presence of numerous bombs and crystal fragments. Only five separate lava flows belonging to the second stage have been found. It seems that volcanic activity ended on Prince Edward few thousands years ago.
The island, annexed by South Africa in 1948, has no human occupation. Only occasional visits for scientific purposes are allowed and all possible measures are taken to keep it in virgin condition, free of man interference.
My Contact Information
Links to Other Sites